Methods: Four provisional restoration biomaterials, namely poly(methyl methacrylate)(DuraLay, Illinois, USA), poly(ethyl methacrylate) (Trim II, Illinois, USA), bis-acrylic composites (Luxatemp Star, Hamburg, Germany and Protemp 4, Seefeld, Germany) were selected for this laboratory investigation. Rectangular specimen beams with the dimensions of 25 mm x 2 mm x 2 mm were prepared using a stainless steel mould according to the manufacturers' instructions. Next, the specimens were chemically cured either in room temperature (23°C) or in a water bath at 100°C for 1 min. Ten specimens per experimental group were subjected to thermo-cycling (3000 cycles, between 5-55°C,with an immersion time of 20 s). Flexural strength of each specimen was determined by 3-point bending test at crosshead speed of 1 mm/min. Data was analyzed using 2-sample t-test and 2-way ANOVA.
Results: The mean flexural strength (±SD) of DuraLay, Trim II, Luxatemp Star and Protemp 4 were 73.31±7.89MPa, 41.79±5.09MPa, 106.20±27.16MPa and 87.50±9.76MPa, respectively (p=0.003). Heat treatment reduced substantially the mean flexural strength of DuraLay (55.65MPa vs.73.31MPa; p<0.001) and Trim II (3.62MPa vs. 41.79MPa; p<0.001) by 24% and 91%, respectively. Heat treatment had no significant effects on Luxatemp Star (106.20MPa vs. 96.14MPa; p<0.383), but it increased the mean flexural strength of Protemp 4 (107.87MPa vs. 87.05MPa; p<0.001) by 23%.
Conclusions: In this laboratory study, the two bis-acryl resin composites exhibited superior flexural strength than poly(methyl methacrylate) and poly(ethyl methacrylate) resins. Heat treatment using a water bath at 100°C for 1 min adversely affected the flexural strength of poly(methyl methacrylate) and poly(ethyl methacrylate) resins, but it enhanced flexural strength of a bis-acrylic composite.